CNT bundle material for flywheels 40 times better than batteries

In the lab, China has small quantities of carbon nanotube bundles 20 times stronger than Kevlar. These are ultralong (several centimeters) carbon nanotube fibers have been made into stronger bundles. The tensile strength of CNTBs (Carbon nanotube bundles) is at least 9–45 times that of other materials. If a more rigorous engineering definition is used, the tensile strength of macroscale CNTBs is still 5–24 times that of any other types of engineering fiber, indicating the extraordinary advantages of ultralong Carbon nanotubes in fabricating superstrong fibers.

A synchronous tightening and relaxing (STR) strategy improves the alignment of the carbon nanotubes to increase the strength.

Tsinghua University researchers are trying to get the fiber into mass production for use in military or other areas.

The material would be very useful for sports equipment, ballistic armor, aeronautics, astronautics and even space elevator.

Ultimate Flywheels with twenty times the energy density 10,000 Watt hours per kilogram

If the material could be used in flywheels for energy storage the energy density would 40 times more than lithium-ion batteries. Electric cars with carbon nanotube bundle flywheels would have a range of 10,000 miles.

Super carbon nanotube bundle flywheels would likely first be used to provide bursts of power for railguns and combat lasers.

The fiber would need to be several kilometers long to make a useful energy storage device.

Flywheels were used in formula one races to provide extra power on turns and for overtaking other race cars. There was some use in 2008 to 2010 and then they were banned in 2011.

Flywheels have been shown to have excellent aging characteristics, with cycle lifetimes in excess of 1,000,000 cycles, regardless of charge rate and depth of discharge.

Superconducting carbon nanotube flywheels

Boeing and Japanese companies have been working on superconducting bearing flywheels for several years. In 2012, Boeing flywheel tip speed was 800 m/sec. World record on small test rotor in 2012 was about 1,405 m/sec. FW tip speed is limited by material properties.

The Boeing plan was trying to develop new materials that would allow speed to reach 3,000 m/sec. The carbon nanotube bundles would allow tip speeds that were twenty or forty times faster.

Boeing has the vision of combining advanced fiber technology and superconducting bearings to enable the development of a low-cost, extremely high energy-density, highefficiency flywheel energy-storage system. The superconducting bearings enable high efficiency and high spin rates. The new proprietary fiber enables high rotor tip speeds resulting in high energy density, with a projected cost of $100/kWh for the flywheel system at utility scale and large-rate factory production. The prototype flywheel will be small enough (7 kWh/5kW) to facilitate rapid development with a design that is easily scalable to a utility-size unit (~100 kWh) and amenable to factory production to achieve low cost. The vision for commercial production is that individual 100-kWh flywheels will be arrayed in a transportable container with a total storage of 2 MWh for utility applications. The Boeing vision is with current weaker materials.

Full strength utility flywheels with the new materials could provide individual flywheels with tens of megawatt hours in power.

 

 

Power-thru uses magnetic levitation with no bearings.

All-composite rotors — versus steel hub and composite overlay — offer lighter weight and reportedly improve safety. The lighter weight also improves energy storage, as POWERTHRU explains: “Kinetic energy is roughly equal to mass times velocity squared. So doubling mass doubles energy storage, but doubling the rotational speed quadruples energy storage.” Thus, today’s all-composite rotors allow faster rotational speed (40,000 to 60,000 rpm), which increases short-term energy storage capacity.

145 thoughts on “CNT bundle material for flywheels 40 times better than batteries”

  1. Planes are over engineered power-wise for takeoff; if you could stick some of these in sort of “shoes” that go over the landing gear, you could accelerate the airplane to takeoff speed and then leave the “shoes” behind. A rough approximation of an aircraft carrier catapult launch. You would probably need to reinforce the landing gear, so the price/performance of that becomes a factor.

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  2. To elaborate why high temperature superconductor bearings are attractive with energy flywheels the parasitic losses of mechanical bearings are about: 5% of the total storage capacity per hour 1% for electromagnetic bearings 0.1% by using high temperature superconductor bearings

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  3. I would greatly prefer to not put the super high RPM flywheel in a moving car/airplane unless you are going to isolate it from all rotation of the car itself.

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  4. Planes are over engineered power-wise for takeoff; if you could stick some of these in sort of shoes”” that go over the landing gear”””” you could accelerate the airplane to takeoff speed and then leave the “”””shoes”””” behind. A rough approximation of an aircraft carrier catapult launch. You would probably need to reinforce the landing gear”””” so the price/performance of that becomes a factor.”””

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  5. To elaborate why high temperature superconductor bearings are attractive with energy flywheels the parasitic losses of mechanical bearings are about:5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the total storage capacity per hour1{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} for electromagnetic bearings0.1{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} by using high temperature superconductor bearings

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  6. I would greatly prefer to not put the super high RPM flywheel in a moving car/airplane unless you are going to isolate it from all rotation of the car itself.

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  7. So advanced fuel cells get 0.9 kwhr/kg. I’ve been saying 1.0 kwhr/kg for years. So since my math is rather close to their math I can say that the primary weight issue for advanced fuel cells comes from heavy fuel tanks. Its something like 95% of the weight of the whole system. I’d bet that you could make that tank lighter with some super awesome carbon nano tubes. Maybe get up to 2.0 kwhr/kg.

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  8. That wouldn’t provide that much power to the plane, just up to takeoff speed. You could do that with a catapult system and no fancy nanotubes.

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  9. Electric cars with carbon nanotube bundle flywheels would have a range of 10,000 miles.” If you’re using flywheels as energy storage in cars, you might as well use the mechanical energy directly instead of mechanical-electrical-mechanical conversion with huge losses…

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  10. With high temperature superconductors you could probably just use an wire loop to store power. yes for large scale storage it would be better. And current losses is not an issue for racing cars or buses who brakes and accelerate all the time.

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  11. So advanced fuel cells get 0.9 kwhr/kg. I’ve been saying 1.0 kwhr/kg for years.So since my math is rather close to their math I can say that the primary weight issue for advanced fuel cells comes from heavy fuel tanks. Its something like 95{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the weight of the whole system.I’d bet that you could make that tank lighter with some super awesome carbon nano tubes. Maybe get up to 2.0 kwhr/kg.

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  12. That wouldn’t provide that much power to the plane just up to takeoff speed. You could do that with a catapult system and no fancy nanotubes.

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  13. Electric cars with carbon nanotube bundle flywheels would have a range of 10″000 miles.””If you’re using flywheels as energy storage in cars”””” you might as well use the mechanical energy directly instead of mechanical-electrical-mechanical conversion with huge losses…”””

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  14. With high temperature superconductors you could probably just use an wire loop to store power. yes for large scale storage it would be better. And current losses is not an issue for racing cars or buses who brakes and accelerate all the time.

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  15. Hmm that might be interesting. Another issue is that they’ll act as gyroscopes, so you need to put them in pairs, rotating opposite directions. Not necessarily a showstopper but the design might get complicated.

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  16. The biggest gain would come weight savings (and perhaps drag savings) by being able to use smaller engines. Anyone knows what % power an aircraft throttles down to for cruising? Are there any other use cases than take-off that needs full power? I read once that the amount of fuel a plane spends on taxing can be quite a lot. The solution then was about towing the planes around. This is pretty low-tech and maybe now with self driving AIs, it can be made profitable. Another passive way to save energy and introduce regenerative braking of an aircraft would be to build the airports with a steeply sloping runway. Then the planes would reuse their own kinetic energy otherwise turned into waste heat during landing. Such an airstrip will be much shorter than current horizontal designs. Could make sense if there is a mountain to piggy back on. Level the top of the mountain to make room for terminal buildings and use the material for the slope. Biggest obstacle to that is probably related to economics. Market economy isn’t good at huge scale infrastructure projects. Maybe China could do it. No flywheels in any of that but the CNT bundles would have many other applications in aircraft.

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  17. Super flywheel are not suitable for moving applications as main power accumulator. The angular momentum conservation law will make almost ungovernable the plane (or car). This device is of interest for fast short burst of power.

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  18. Hmm that might be interesting. Another issue is that they’ll act as gyroscopes so you need to put them in pairs rotating opposite directions. Not necessarily a showstopper but the design might get complicated.

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  19. The biggest gain would come weight savings (and perhaps drag savings) by being able to use smaller engines. Anyone knows what {22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} power an aircraft throttles down to for cruising?Are there any other use cases than take-off that needs full power?I read once that the amount of fuel a plane spends on taxing can be quite a lot. The solution then was about towing the planes around. This is pretty low-tech and maybe now with self driving AIs it can be made profitable.Another passive way to save energy and introduce regenerative braking of an aircraft would be to build the airports with a steeply sloping runway. Then the planes would reuse their own kinetic energy otherwise turned into waste heat during landing. Such an airstrip will be much shorter than current horizontal designs. Could make sense if there is a mountain to piggy back on. Level the top of the mountain to make room for terminal buildings and use the material for the slope. Biggest obstacle to that is probably related to economics. Market economy isn’t good at huge scale infrastructure projects. Maybe China could do it.No flywheels in any of that but the CNT bundles would have many other applications in aircraft.

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  20. Super flywheel are not suitable for moving applications as main power accumulator. The angular momentum conservation law will make almost ungovernable the plane (or car).This device is of interest for fast short burst of power.

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  21. Supposedly in energy density. Stronger materials -> higher max RPM -> higher energy density. Haven’t done the math though, so don’t know if 40 is correct.

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  22. If most of the weight is in the fuel (as it should be), then making the tank lighter won’t make much of a difference. Different story with launch vehicles though, where you’re fighting gravity and are bound by the rocket equation. There, every kg you save on the structure is a kg you can add to the payload.

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  23. If you google for Cubli, it uses flywheels to jump, rotate, etc. There are youtube videos of it. So one could potentially make a very maneuverable vehicle.

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  24. The flywheels can be paired to rotate in opposite directions. If rotational inertia is still an issue, with some clever engineering it may be possible to use the flywheels to augment steering, rather than interfere with it.

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  25. Supposedly in energy density. Stronger materials -> higher max RPM -> higher energy density. Haven’t done the math though so don’t know if 40 is correct.

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  26. If most of the weight is in the fuel (as it should be) then making the tank lighter won’t make much of a difference. Different story with launch vehicles though where you’re fighting gravity and are bound by the rocket equation. There every kg you save on the structure is a kg you can add to the payload.

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  27. If you google for Cubli it uses flywheels to jump rotate etc. There are youtube videos of it. So one could potentially make a very maneuverable vehicle.

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  28. The flywheels can be paired to rotate in opposite directions. If rotational inertia is still an issue with some clever engineering it may be possible to use the flywheels to augment steering rather than interfere with it.

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  29. Engines do almost all of their work getting a plane to altitude. No way you would tow planes around with cold engines. You want to know that your engines are running and don’t want to waste time starting them when you are ready for takeoff. Sloping runways are a deathtrap. In general you want a longer, flat runway so that if you lose an engine on takeoff you can brake instead of going over a mountain cliff. The modern airline industry has 5 nines reliability (one crash per 100,000 flights). Any gimmicks you introduce will result in deaths.

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  30. Pairing “gyros” would result in an overall net zero moment of angular inertia for the overall system but each flywheel is still torquing every time you go over a bump. Just not the best idea.

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  31. If you want fuel cell airplanes then the weight is an issue. Of course I don’t quite know why you need fuel cell airplanes but it is a superior option to battery airplanes.

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  32. Engines do almost all of their work getting a plane to altitude.No way you would tow planes around with cold engines. You want to know that your engines are running and don’t want to waste time starting them when you are ready for takeoff.Sloping runways are a deathtrap.In general you want a longer flat runway so that if you lose an engine on takeoff you can brake instead of going over a mountain cliff.The modern airline industry has 5 nines reliability (one crash per 100000 flights). Any gimmicks you introduce will result in deaths.

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  33. Pairing gyros”” would result in an overall net zero moment of angular inertia for the overall system but each flywheel is still torquing every time you go over a bump. Just not the best idea.”””

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  34. If you want fuel cell airplanes then the weight is an issue.Of course I don’t quite know why you need fuel cell airplanes but it is a superior option to battery airplanes.

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  35. 95{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the weight is the fuel tank. The fuel itself is trivial and almost a rounding error.

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  36. Yes it was me who pointed out that SOFC’s are crazy bad for power density.

    I’m not really advocating fuel cell airplanes. I’m certainly not advocating BEV planes. Jet fuel is basically superior for anything long haul and it isn’t close.

    But if you want a EV plane for some reason then fuel cells are better than batteries because the specific power is 5-10x better than batteries and refueling is much faster and easier than battery swapping.

    The point being that most of the weight of the fuel cell solution is in heavy tankage. Now if you can make your tanks from crazy strong nanotubes then you can make the tank lighter and potentially double, triple, or quadruple the specific power of the powerplant stack and have an EV plane with a specific power of say 4kwhr/kg which would be amazing.

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  37. I prefer the new solid state Li-Ion baterry reinvented by profesor Jhon B. Goodenoght and Helena Braga.
    Imagine what happen when you see ice on the street samething like one HDD do in your hand when is working you can feel the rotation… Imagine that at high speed + high weight, no thank you.
    That is good i think for power station to reduce fluctuation of entire national electric red.

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  38. I thought the classical thin walled cylinder was the ideal shape, though that distorts into a thick rectangular cross-section torus in practical setups, along with the necessary radial arms to connect to the shaft?

    What is the functional difference between a tapered block, and a series of tapered wafers then?

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  39. My understanding is only the outer layer of the flywheel will be covered in CNT.
    And I am assuming the outer case will be covered in CNT as well for safety, in case flywheel flies apart.

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  40. Let’s see, neglecting the interaction between volume elements, for a volume element dV = dA*dr at distance r from the axis and angular velocity w:

    v = w*r (tangential velocity, [m/s])
    m = ro*dV (ro = density, [kg/m^3])

    Ek = 0.5*m*v^2 = 0.5*ro*dV*(w*r)^2 [J]
    Esp = Ek/m = 0.5*v^2 = 0.5*(w*r)^2 (specific energy, [J/kg])

    Fr = m*v^2/r = ro*dV*(w*r)^2/r = ro*dV*w^2*r (radial force, [N])
    Lr = Fr/dA = Fr*dr/dV = (ro*dV*w^2*r)*dr/dV = ro*w^2*r*dr (radial load, [Pa])
    Yrsp = Lrsp = Lr/ro = w^2*r*dr (specific radial load, directly comparable to specific yield strength, [N*m/kg])

    Esp/Yrsp = [0.5*(w*r)^2] / [w^2*r*dr] = 0.5*r/dr ([J/N*m] aka unitless)

    dr is constant, so assuming purely radial loads, for any given specific yield strength Ysp, the maximum specific energy is proportional to the radius. This suggests that you *do* want a torus.

    What if we assume the fibers arranged in a circumferential loop, with the loads translated to tangential loads? The hoop stress of a thin-walled cylinder of wall thickness t = dr and radius r, under internal pressure P = Lr, is:

    Lt = P*r/t (Lt = tangential load = hoop stress, [Pa])
    Lt = Lr*r/dr = (ro*w^2*r*dr)*r/dr = ro*(w*r)^2
    Ytsp = Ltsp = Lt/ro = (w*r)^2 (specific tangential load, directly comparable to specific yield strength, [N*m/kg] = [m^2/s^2])

    Esp/Ytsp = [0.5*(w*r)^2] / (w*r)^2 = 0.5 ([J/N*m] aka unitless)

    Based on this, under pure hoop load, both load and energy scale quadratically with radius, so the maximum specific energy depends only on the specific yield strength, regardless of mass distribution.

    I may have missed some mathematical nuances, and maybe the interaction between volume elements does need to be accounted for, but my conclusion from this is that you *do* want a torus, or rather, a cylindrical shell.

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  41. “You DEFINITELY DO NOT WANT your flywheels shaped like a big torus, whether rectangular in cross section or circular like a donut. The energy dynamics is 6.8× worse, kilogram per kilogram.
    What is needed instead is a perforated shaft (lots and lots of round drillings, chamfered nicely), through which is embedded a long thin rod made of the CWNT material.”

    How about a plain cylinder?

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  42. A secondary one at best. Hauling huge hydrogen tanks is unrealistic. And I think it was you who pointed out that SOFCs have way too low power density.

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  43. Hmm, this doesn’t really work out. From my notes, both kevlar and CFRP are ~2e6 [N*m/kg] specific UTS, so let’s say about half that specific yield. That works out to ~100 [kW/kg], which is much higher than what they’re getting, isn’t it?

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  44. If I get that right, your equation is: k1*ro = Y/Esp, where k1 is you “magic factor” of 10.8 [L*MPa/kWh], ro is density in [kg/L], Y is the yield strength in [MPa], and Esp is the specific energy capacity in [kWh/kg].

    In engineering we like to work with specific properties, so to convert that to specific tensile strength, first we need to adjust ro to [kg/m^3] and Y to [Pa]. That gives k2*ro = Y/Esp, where k2 = 10.8 [L*MPa/kWh] * 1000000 [Pa/MPa] / 1000 [L/m^3] = 10800 [m^3*Pa/kWh] or [N*m/kWh]. We then divide both sides by ro, to get k2 = Ysp/Esp where Ysp is the specific yield strength in [Pa*m^3/kg] aka [N*m/kg].

    I think [N*m/kWh] is more sensible than some weird [L*MPa/kWh], and 10800 is pretty easy to remember. If we want to go back to proper metric and Esp in [MJ/kg], then k3 = 10800 [N*m/kWh] * 1000 [kW/MW] / 3600 [s/h] = 3000 [N*m/MJ], which is even easier to remember.

    In summary, Ysp/Esp = 10800 [N*m/kWh] = 3000 [N*m/MJ] (the 1/kg in Ysp and Esp cancel out)

    (I was also going to ask whether a different flywheel structure would alter the result, but I saw you already addressed that in another post.)

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  45. Hmm yea I thought about the issue of high-RPM/gearing incompatibility but dismissed it with “there’s got to be some clever way to engineer it efficiently”.

    But I agree that in general I wouldn’t want a flywheel as main energy storage inside a regular car.

    Military applications seem more interesting.

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  46. So, your car would corner really flat. You’d have to gimbal the housing 25 degrees in the x, and y axes or so to allow for steep hills, and banking, but the car would be difficult to flip over. Once you hit the end of travel, the flywheel would resist rotation..

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  47. Engines do almost all of their work getting a plane to altitude. No way you would tow planes around with cold engines. You want to know that your engines are running and don’t want to waste time starting them when you are ready for takeoff. Sloping runways are a deathtrap. In general you want a longer, flat runway so that if you lose an engine on takeoff you can brake instead of going over a mountain cliff. The modern airline industry has 5 nines reliability (one crash per 100,000 flights). Any gimmicks you introduce will result in deaths.

    Reply
  48. Engines do almost all of their work getting a plane to altitude.No way you would tow planes around with cold engines. You want to know that your engines are running and don’t want to waste time starting them when you are ready for takeoff.Sloping runways are a deathtrap.In general you want a longer flat runway so that if you lose an engine on takeoff you can brake instead of going over a mountain cliff.The modern airline industry has 5 nines reliability (one crash per 100000 flights). Any gimmicks you introduce will result in deaths.

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  49. I assume they are writing about kWh/kg. The turnaround, or the electrical energy discharged/charged is also much better than batteries, particularly at high currents.
    I think this is an interesting solution for static applications. I don’t think I’d put a high energy density flywheel in a car. I’d a lot rather have a battery fire, than have one of these things undergo unplanned energetic disassembly during an auto crash. How much would the housing have to weigh to be safe?
    Fully charged, the edge speed would be at least several kilometers per second, push the technology a bit, and you might have the edge traveling at escape velocity(10.73 km/sec), a few feet away from your feet.

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  50. Pairing “gyros” would result in an overall net zero moment of angular inertia for the overall system but each flywheel is still torquing every time you go over a bump. Just not the best idea.

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  51. Pairing gyros”” would result in an overall net zero moment of angular inertia for the overall system but each flywheel is still torquing every time you go over a bump. Just not the best idea.”””

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  52. If you want fuel cell airplanes then the weight is an issue. Of course I don’t quite know why you need fuel cell airplanes but it is a superior option to battery airplanes.

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  53. If you want fuel cell airplanes then the weight is an issue.Of course I don’t quite know why you need fuel cell airplanes but it is a superior option to battery airplanes.

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  54. 95{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the weight is the fuel tank. The fuel itself is trivial and almost a rounding error.

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  55. The “take away from Goat’s calculus” is easy to remember:

    ⇒ performance = 10.8 times density of flywheel material in MPa per kWh.

    That’s it. 10.8ρ
    Say a ρ about 1.5 times heavier than water.

    ⇒ 1.5 kg/lliter
    … 1500 kg/m³

    ⇒ performance = 10.8 × 1500
    … = 16,200 MPa/kWh

    What that in turn implies is a simple relationship between what your novel material is rated at — tensile strength — and how its maximum safe stress converts to kilowatt hours of stored rotational energy.

    Its that simple.
    Just saying,
    GoatGuy

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  56. PS… one more thing.

    You DEFINITELY DO NOT WANT your flywheels shaped like a big torus, whether rectangular in cross section or circular like a donut. The energy dynamics is 6.8× worse, kilogram per kilogram.

    What is needed instead is a perforated shaft (lots and lots of round drillings, chamfered nicely), through which is embedded a long thin rod made of the CWNT material. Radially, your shaft has hundreds of these rods, all very carefully balanced and affixed positively.

    Alternatively, one might imagine having a fabricator create thick-in-the-center-thin-at-the-edges wafers of the CWNT material, with VERY little binding (since it increases mass, but decreases performance to lack of adhesive strength). Stack them on a square shaft. This has the advantage of being able to make the wafers externally, balance them, and certify them to 25% higher-than-rated rotation speed.

    But in any case, we do NOT want a square or round cross section torus spinning about a shaft axis.

    Calculus shows the results quite well.
    6.9× higher forces required per kWh (per kilogram) of flywheel material for tori.

    Just saying,
    GoatGuy

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  57. Oh, Lord. No.
    No, no, no, no … no.

    Flywheels — if we ever get them having this article’s claimed numbers — will be levitated by passive fail-safe bearings. The mechanical power-tap and power-spin-up mechanism will be a magnetic A/C coupling. Again, nothing touching. Moreover, the whole thing will run in a vacuum, to almost eliminate parasitic air-friction losses.

    After all, its going to be spinning at 250,000 RPM.

    The magic of modern electronics will convert the A/C dynamo power into whatever the motors-that-push-the-wheels require. Just like in all modern cars.

    Just saying,
    GoatGuy

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  58. With few exceptions, the HIGHER the rotational rate of motors (or for static things like the frequency of transformers) generally the higher the efficiency. You DEFINITELY don’t want anything geared or toothed touching a rotor spinning at 250,000 RPM. Ever.

    As to 10,000 miles?

    That’s easy enough… since 1 kWh equals about 2.5 to 5 motive miles (depending on how heavy is the car, how well streamlined it is, how pressurized the tires and all that), and we say 3.5 miles generally, then

    ⇒ 10,000 miles ÷ 3.5 miles per kWh
    … = 2,857 kWh
    … ≈ 3,000 kWh (× 3.6×10⁶ J/kWh, ÷ 4186000 J/kg TNT)
    … ≈ 2,500 kg of TNT

    Now, I don’t know about you, but I’m CERTAIN as a regulator of such things, that I wouldn’t EVER let ordinary consumers cart around 2,500 kilograms or 2½ tons of TNT in their cars. Nominally. You could take out a parking garage with that much explosive. Or if you’ve got a line of cars in the garage, all with 2,500 kg of TNT stored energy, the chain reaction would be nearly nuclear.

    Then there’s the “real mss”. Even if the raw CWNT material is rated at 50 GPa WORKING stress, even if so, it takes 0.32 kg per kWh of CWNT, and very probably 10× that for protective enclosure. So…

    ⇒ 3,000 kWh • (0.32 ⊕ 3.2) → 10,500 kg.

    Again, I really don’t think that people are going to be driving around 10 tons of flywheel setup to get 10,000 miles of range. I just don’t. Maybe like the Tesla Model S, with its 1300 lb battery (600 kg), they’ll settle on a 600 kg flywheel giving them 600 miles range.

    Just saying.

    We tech-article commenters REALLY have to do math, you know?
    Real, hard, straight forward math.
    Dollar store calculator math.
    By 7th graders.

    Sheesh.
    GoatGuy

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  59. That sounds like an urban myth.

    But it does kind of underline something I wrote earlier in the other flywheels-here-we-come article. Namely, that flywheel strands are under enormous tension when spinning at top-rated speed. In one o those lovely “I’m doing calculus to prove this” moments, I found that:

    ⇒ perf = 3 ρ … in Pa⋅kg/J, with scale conversions
    ⇒ perf = 3.6 × 3 ρ … in MPa⋅kg/kWh

    Now that is an interesting finding. It shows that the performance of a material depends entirely on its density. I was using 1500 kg/m³ (1.5 kg/L or 1.5 g/ml) as the “heavier than water, lighter than any metal” density for superior carbon fibers.

    Using that:

    ⇒ perf = 3.6 × 3 × 1500
    ⇒ perf = 16,200 MPa⋅kg/kWh

    Meaning, that we can work it any way you want: you have a material that has a maximum working stress (tension) of 50,000 MPa? OK:

    ⇒ 50,000 MPa ÷ 16,200 MPa⋅kg/kWh
    ⇒ 3.08 kWh/kg

    Or, work it backward. You desire 2.5 kWh/kg in order to, with fabrication of enclosures and so on, come up with a light duty working unit offering 1.0 kWh/kg of all-in mass.

    ⇒ 2.5 kWh/kg × 16,200 MPa⋅kg/kWh
    ⇒ 40,500 MPa

    That — 40 gigapascals — is about 20× the maximum working tensile stress that Kevlar(™) can withstand in year-after-year working force. I argue that that’s about the top one might get out of carbon nanotube tape, with precisely and esquisitely perfect tape … and all the overlapping and so on that a real fabricated rotor would entail.

    I’ve been at “materials science” for many a decade now. 40+ gigapascal working tension is absolutely mind-bogglingly high.
    ________________________________________

    PS: in turn, one then needs to use the actual dimensions of our “design rotor” to decide things such as rotational speed, cross-section figure, and all that.

    Again, as a for instance, using the formula (thank you calculus!):

    ⇒ L = 0.3 m (the radius of the rotor’s carbon fibers)
    ⇒ ω = 1,500 kg/m³ (from above)

    ⇒ F = ⅛ρπω²d²L²
    … ω = √( 40,500,000,000 × 8 ÷ 1,500 / π ÷ 0.3² )
    … ω = ( 27,640 rad/s ) ÷ 2π × 60
    … ω = 264,000 RPM

    See what I mean? well over a quarter million RPM, with a rotor whose strands are nearly 2 feet long, each. Since we specified 2.5 kg/kWh at the outset, its easy to scale for our (hoped for) 100 kWh (for automative use).

    ⇒ mass = 100 kWh ÷ 2.5 kWh/kg
    … mass = 40 kg.

    Remember that rotor stacks some REAL energy kinetically.

    ⇒ TNT energy = Ek ÷ 4186 J/g of TNT
    … TNT energy = (100 kWh × 3.6×10⁶ J/kWh) ÷ 4186 J/g TNT
    … TNT energy = 86,000 g. ⇒ 86 kg TNT.

    I’ll betcha that this device’s containment shroud will be REALLY well armored. That’s a lot of Kaboom.

    Just saying,
    GoatGuy

    Reply
  60. Supposedly in energy density. Stronger materials -> higher max RPM -> higher energy density. Haven’t done the math though, so don’t know if 40 is correct.

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  61. Supposedly in energy density. Stronger materials -> higher max RPM -> higher energy density. Haven’t done the math though so don’t know if 40 is correct.

    Reply
  62. If most of the weight is in the fuel (as it should be), then making the tank lighter won’t make much of a difference. Different story with launch vehicles though, where you’re fighting gravity and are bound by the rocket equation. There, every kg you save on the structure is a kg you can add to the payload.

    Reply
  63. If most of the weight is in the fuel (as it should be) then making the tank lighter won’t make much of a difference. Different story with launch vehicles though where you’re fighting gravity and are bound by the rocket equation. There every kg you save on the structure is a kg you can add to the payload.

    Reply
  64. If you google for Cubli, it uses flywheels to jump, rotate, etc. There are youtube videos of it. So one could potentially make a very maneuverable vehicle.

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  65. If you google for Cubli it uses flywheels to jump rotate etc. There are youtube videos of it. So one could potentially make a very maneuverable vehicle.

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  66. The flywheels can be paired to rotate in opposite directions. If rotational inertia is still an issue, with some clever engineering it may be possible to use the flywheels to augment steering, rather than interfere with it.

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  67. The flywheels can be paired to rotate in opposite directions. If rotational inertia is still an issue with some clever engineering it may be possible to use the flywheels to augment steering rather than interfere with it.

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  68. There must of course be a horizontal stretch at the end of the strip facing away from the terminal buildings and gates. The slope only needs to be dimensioned so the aircraft reaches ~terminal velocity when accelerating down to the horizontal part.

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  69. Hmm that might be interesting. Another issue is that they’ll act as gyroscopes, so you need to put them in pairs, rotating opposite directions. Not necessarily a showstopper but the design might get complicated.

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  70. Hmm that might be interesting. Another issue is that they’ll act as gyroscopes so you need to put them in pairs rotating opposite directions. Not necessarily a showstopper but the design might get complicated.

    Reply
  71. The biggest gain would come weight savings (and perhaps drag savings) by being able to use smaller engines. Anyone knows what % power an aircraft throttles down to for cruising? Are there any other use cases than take-off that needs full power? I read once that the amount of fuel a plane spends on taxing can be quite a lot. The solution then was about towing the planes around. This is pretty low-tech and maybe now with self driving AIs, it can be made profitable. Another passive way to save energy and introduce regenerative braking of an aircraft would be to build the airports with a steeply sloping runway. Then the planes would reuse their own kinetic energy otherwise turned into waste heat during landing. Such an airstrip will be much shorter than current horizontal designs. Could make sense if there is a mountain to piggy back on. Level the top of the mountain to make room for terminal buildings and use the material for the slope. Biggest obstacle to that is probably related to economics. Market economy isn’t good at huge scale infrastructure projects. Maybe China could do it. No flywheels in any of that but the CNT bundles would have many other applications in aircraft.

    Reply
  72. The biggest gain would come weight savings (and perhaps drag savings) by being able to use smaller engines. Anyone knows what {22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} power an aircraft throttles down to for cruising?Are there any other use cases than take-off that needs full power?I read once that the amount of fuel a plane spends on taxing can be quite a lot. The solution then was about towing the planes around. This is pretty low-tech and maybe now with self driving AIs it can be made profitable.Another passive way to save energy and introduce regenerative braking of an aircraft would be to build the airports with a steeply sloping runway. Then the planes would reuse their own kinetic energy otherwise turned into waste heat during landing. Such an airstrip will be much shorter than current horizontal designs. Could make sense if there is a mountain to piggy back on. Level the top of the mountain to make room for terminal buildings and use the material for the slope. Biggest obstacle to that is probably related to economics. Market economy isn’t good at huge scale infrastructure projects. Maybe China could do it.No flywheels in any of that but the CNT bundles would have many other applications in aircraft.

    Reply
  73. Super flywheel are not suitable for moving applications as main power accumulator. The angular momentum conservation law will make almost ungovernable the plane (or car). This device is of interest for fast short burst of power.

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  74. Super flywheel are not suitable for moving applications as main power accumulator. The angular momentum conservation law will make almost ungovernable the plane (or car).This device is of interest for fast short burst of power.

    Reply
  75. These are not new. General Atomics developed such storage to an advanced level, and did so over a decade ago. They too used magnetic levitation — essential due to the speeds involved.

    They stopped the program when their primary flywheel flew apart during a demonstration test, taking with it all the scientists gathered therein, as well as a good portion of the building. They might have continued, but they had no scientists left sufficiently knowledgeable to do so.

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  76. Engines do almost all of their work getting a plane to altitude.
    No way you would tow planes around with cold engines. You want to know that your engines are running and don’t want to waste time starting them when you are ready for takeoff.
    Sloping runways are a deathtrap.
    In general you want a longer, flat runway so that if you lose an engine on takeoff you can brake instead of going over a mountain cliff.

    The modern airline industry has 5 nines reliability (one crash per 100,000 flights). Any gimmicks you introduce will result in deaths.

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  77. Pairing “gyros” would result in an overall net zero moment of angular inertia for the overall system but each flywheel is still torquing every time you go over a bump. Just not the best idea.

    Reply
  78. If most of the weight is in the fuel (as it should be), then making the tank lighter won’t make much of a difference. Different story with launch vehicles though, where you’re fighting gravity and are bound by the rocket equation. There, every kg you save on the structure is a kg you can add to the payload.

    Reply
  79. The flywheels can be paired to rotate in opposite directions. If rotational inertia is still an issue, with some clever engineering it may be possible to use the flywheels to augment steering, rather than interfere with it.

    Reply
  80. Hmm that might be interesting.

    Another issue is that they’ll act as gyroscopes, so you need to put them in pairs, rotating opposite directions. Not necessarily a showstopper but the design might get complicated.

    Reply
  81. The biggest gain would come weight savings (and perhaps drag savings) by being able to use smaller engines. Anyone knows what % power an aircraft throttles down to for cruising?
    Are there any other use cases than take-off that needs full power?

    I read once that the amount of fuel a plane spends on taxing can be
    quite a lot. The solution then was about towing the planes around. This is pretty low-tech and maybe now with self driving AIs, it can be made profitable.

    Another passive way to save energy and introduce regenerative braking of an aircraft would be to build the airports with a steeply sloping runway. Then the planes would reuse their own kinetic energy otherwise turned into waste heat during landing. Such an airstrip will be much shorter than current horizontal designs. Could make sense if there is a mountain to piggy back on. Level the top of the mountain to make room for terminal buildings and use the material for the slope. Biggest obstacle to that is probably related to economics. Market economy isn’t good at huge scale infrastructure projects. Maybe China could do it.

    No flywheels in any of that but the CNT bundles would have many other applications in aircraft.

    Reply
  82. Super flywheel are not suitable for moving applications as main power accumulator. The angular momentum conservation law will make almost ungovernable the plane (or car).
    This device is of interest for fast short burst of power.

    Reply
  83. So advanced fuel cells get 0.9 kwhr/kg. I’ve been saying 1.0 kwhr/kg for years. So since my math is rather close to their math I can say that the primary weight issue for advanced fuel cells comes from heavy fuel tanks. Its something like 95% of the weight of the whole system. I’d bet that you could make that tank lighter with some super awesome carbon nano tubes. Maybe get up to 2.0 kwhr/kg.

    Reply
  84. So advanced fuel cells get 0.9 kwhr/kg. I’ve been saying 1.0 kwhr/kg for years.So since my math is rather close to their math I can say that the primary weight issue for advanced fuel cells comes from heavy fuel tanks. Its something like 95{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the weight of the whole system.I’d bet that you could make that tank lighter with some super awesome carbon nano tubes. Maybe get up to 2.0 kwhr/kg.

    Reply
  85. That wouldn’t provide that much power to the plane, just up to takeoff speed. You could do that with a catapult system and no fancy nanotubes.

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  86. That wouldn’t provide that much power to the plane just up to takeoff speed. You could do that with a catapult system and no fancy nanotubes.

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  87. Electric cars with carbon nanotube bundle flywheels would have a range of 10,000 miles.” If you’re using flywheels as energy storage in cars, you might as well use the mechanical energy directly instead of mechanical-electrical-mechanical conversion with huge losses…

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  88. Electric cars with carbon nanotube bundle flywheels would have a range of 10″000 miles.””If you’re using flywheels as energy storage in cars”””” you might as well use the mechanical energy directly instead of mechanical-electrical-mechanical conversion with huge losses…”””

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  89. With high temperature superconductors you could probably just use an wire loop to store power. yes for large scale storage it would be better. And current losses is not an issue for racing cars or buses who brakes and accelerate all the time.

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  90. With high temperature superconductors you could probably just use an wire loop to store power. yes for large scale storage it would be better. And current losses is not an issue for racing cars or buses who brakes and accelerate all the time.

    Reply
  91. Planes are over engineered power-wise for takeoff; if you could stick some of these in sort of “shoes” that go over the landing gear, you could accelerate the airplane to takeoff speed and then leave the “shoes” behind. A rough approximation of an aircraft carrier catapult launch. You would probably need to reinforce the landing gear, so the price/performance of that becomes a factor.

    Reply
  92. Planes are over engineered power-wise for takeoff; if you could stick some of these in sort of shoes”” that go over the landing gear”””” you could accelerate the airplane to takeoff speed and then leave the “”””shoes”””” behind. A rough approximation of an aircraft carrier catapult launch. You would probably need to reinforce the landing gear”””” so the price/performance of that becomes a factor.”””

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  93. To elaborate why high temperature superconductor bearings are attractive with energy flywheels the parasitic losses of mechanical bearings are about: 5% of the total storage capacity per hour 1% for electromagnetic bearings 0.1% by using high temperature superconductor bearings

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  94. To elaborate why high temperature superconductor bearings are attractive with energy flywheels the parasitic losses of mechanical bearings are about:5{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} of the total storage capacity per hour1{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} for electromagnetic bearings0.1{22800fc54956079738b58e74e4dcd846757aa319aad70fcf90c97a58f3119a12} by using high temperature superconductor bearings

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  95. I would greatly prefer to not put the super high RPM flywheel in a moving car/airplane unless you are going to isolate it from all rotation of the car itself.

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  96. I would greatly prefer to not put the super high RPM flywheel in a moving car/airplane unless you are going to isolate it from all rotation of the car itself.

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  97. So advanced fuel cells get 0.9 kwhr/kg. I’ve been saying 1.0 kwhr/kg for years.

    So since my math is rather close to their math I can say that the primary weight issue for advanced fuel cells comes from heavy fuel tanks. Its something like 95% of the weight of the whole system.

    I’d bet that you could make that tank lighter with some super awesome carbon nano tubes. Maybe get up to 2.0 kwhr/kg.

    Reply
  98. “Electric cars with carbon nanotube bundle flywheels would have a range of 10,000 miles.”

    If you’re using flywheels as energy storage in cars, you might as well use the mechanical energy directly instead of mechanical-electrical-mechanical conversion with huge losses…

    Reply
  99. With high temperature superconductors you could probably just use an wire loop to store power.
    yes for large scale storage it would be better.
    And current losses is not an issue for racing cars or buses who brakes and accelerate all the time.

    Reply
  100. Planes are over engineered power-wise for takeoff; if you could stick some of these in sort of “shoes” that go over the landing gear, you could accelerate the airplane to takeoff speed and then leave the “shoes” behind. A rough approximation of an aircraft carrier catapult launch. You would probably need to reinforce the landing gear, so the price/performance of that becomes a factor.

    Reply
  101. To elaborate why high temperature superconductor bearings are attractive with energy flywheels the parasitic losses of mechanical bearings are about:
    5% of the total storage capacity per hour
    1% for electromagnetic bearings
    0.1% by using high temperature superconductor bearings

    Reply

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